Wednesday 17 September 2008 19.01 EDT
First published on Wednesday 17 September 2008 19.01 EDT

The Guardian/Library House CleanTech 100 is an exciting glimpse of the future. The aim is to highlight a group of the most promising private companies in Europe focusing on clean technology, with ­companies selected on the basis of their potential for future growth and ­beneficial environmental impact. With ­climate change and energy use nudging the top of political and commercial ­agendas, these are companies that have a stake in how our world develops.

The list represents a mixed spectrum of companies, reflecting the diversity of technology within the cleantech sector through the "energy chain" - from ­production, through to transmission and storage, to end-user application. ­Typically, companies in the list have leading-edge products and technologies that are just coming to market, or on the verge of commercialisation.

They are potentially the big names of tomorrow, rather than household names of today. But all of the Guardian/Library House CleanTech 100 share the potential for significant growth. And all might have a significant impact on our lives in future.

Indicators

Library House's expertise lies in tracking fast-growth innovation-based private companies in different sectors. An ­initial list of 200 was selected from their CleanTech Intelligence database of private clean tech companies, using various indicators such as each ­company's capital history, ­aggregated positive news stories, and size of ­management team, plus an analyst selection to make sure companies were credible. (Investment-only companies were excluded.)

Expert advisory board members were then invited to nominate further ­companies to ensure the net was thrown widely enough. Finally, to avoid bias, board members were told that at least half their nominations must be ­companies with which they had no affiliation.

The ­advisory panel consisted of some of Europe's most experienced ­investors in the growing area of clean technology - a mix of venture ­capitalists, investment analysts and technology ­lawyers.

Companies were based against two broad criteria: environmental impact and future growth prospects. We asked:

• What is the company's potential for positive environmental impact• What would be the scale of that ­positive impact if the company's ­technology or activity proliferates?• What is the potential market size?• How disruptive (and hence potentially fast-growing) is the technology?• What position does the company have in the market?• What is the company's vision?

To make the process workable, board members were asked to vote for ­companies that they felt best matched the criteria, based on their knowledge of the company and the broader market. Basic company details were circulated to each board member to allow for the first round of voting on the 200, and nomination of new companies.

This helped bring new companies to light, and eliminated others. Next, the board met to finalise the list, producing a top 100. Those receiving the most votes were then put forward for the top 10, which was ranked by the advisory board members in a final round of closed ballot voting.

Though getting venture capital funding - a key step towards wider success - is not essential, many of the companies here have achieved that step because there's a strong correlation between fast-growing companies and those that are venture-funded. The list reflects that: Europe's most active venture capital markets, the UK and Germany, are home to the greatest number of companies.